1. Field of the Invention
The present invention relates to a patterned master carrier for magnetic transfer including a signal pattern on a surface for magnetically transferring a desired magnetization pattern to a slave medium, a manufacturing method thereof, a magnetic transfer method using the master carrier, a recording medium, and a magnetic recording and reproduction apparatus.
2. Description of the Related Art
A magnetic transfer method is conventionally known, in which a patterned master carrier for magnetic transfer carrying signal information in the form of fine uneven pattern of a magnetic material is in close contact with a slave medium (transfer medium) having a magnetic recording layer for receiving the magnetic transfer, and then a magnetization pattern corresponding to the information carried by the master carrier is transferred to and recorded on the slave medium by applying a magnetic field during the magnetic transfer process. This magnetic transfer method can perform recording statically without changing relative positions between the master carrier and the slave medium. The method also has an advantage of a very short time period required for recording (see U.S. Pat. No. 6,347,016, for example).
Along with the recent development of ultra-fine processing techniques, such as electron beam lithography, it is now possible to pattern signals having minimum bit lengths of 100 nm or below, and to perform one-time writing of signals corresponding to a surface density of a current hard disk device by means of the magnetic transfer.
The above-mentioned U.S. patent and the like have already disclosed the use of this magnetic transfer method for recording a head-positioning servo signal on a magnetic recording medium.
Meanwhile, one of the technical problems in the magnetic transfer method is occurrence of an unclear magnetically recorded portion (reverse magnetization) on the slave medium in the course of signal transfer from the master carrier to the slave medium. Since the subpulse is detected from a readout waveform of the magnetization pattern due to existence of this unclear magnetically recorded portion, there is a possibility of occurrence of an error in a magnetic reproduction apparatus which recognizes the subpulse as a reproduction signal. A method of observing the subpulse caused by this unclear magnetically recorded portion is disclosed in Japanese Unexamined Patent Publication No. 2002-42301 and U.S. patent Laid-Open No. 20020044368, for example.
However, the inventors of the present invention have found out that it is possible to suppress the occurrence of the subpulse effectively by use of a magnetic substrate as a substrate for the master carrier and by means of adjusting transfer conditions such as pressure for close contact between the master carrier and the slave medium, and so on.
However, when a transferred signal is a servo signal, for example, it is difficult to completely eliminate subpulses attributable to unclear magnetically recorded portions, which occur on data area sides of adjacent portions in a track direction of servo areas and the data areas on a slave medium after magnetic transfer. An example will be described with reference to schematic drawings in FIGS. 4A to 4C.
FIGS. 4A to 4C are drawings schematically showing part of a cross section in a track direction of a master carrier, a magnetization pattern of a corresponding portion of a slave medium on which the magnetization pattern is transferred from the master carrier, and a readout waveform to be detected from the magnetization pattern. As shown in FIG. 4A, a master carrier 101 comprises a signal pattern including signal areas 102 where uneven shapes based on servo signals are formed and a flat no-signal area 103. This master carrier 101 includes a substrate 101a made of a magnetic material such as Ni which has uneven shape corresponding to the signal pattern on a surface thereof, and a magnetic layer 101b deposited on the signal pattern surface of the substrate 101a. The magnetization pattern as shown in FIG. 4B is transferred to the slave medium by applying the magnetic field having a reverse orientation to an orientation of direct-current magnetization, subjected in advance to a magnetic recording layer of the slave medium in one orientation along tracks, in a state where the surface of this master carrier 101, where the magnetic layer 101b is formed, is brought into close contact with the magnetic recording layer of the slave medium. In this event, unclear magnetically recorded portions 104 are formed on part of the no-signal area adjacent to the signal areas, whereby a readout waveform as shown in FIG. 4C is detected from the magnetization pattern shown in FIG. 4B. As illustrated therein, subpulses 105 are detected in response to the unclear magnetically recorded portions 104. That is, in a magnetic reproduction apparatus for reproducing the magnetic recording medium, there is a risk of a problem where such subpulses are detected and misrecognized as reproduction signals. For example, subpulses occurring on both ends of a servo area may cause a shift of servo timing mark attributable to misrecognition of timing for a start and an end of a servo signal portion, and may cause an error such as servo tracking incapability.
Note that occurrence of the subpulse is not only limited to the case where the signal pattern is made of servo signals. For example, when the magnetic transfer is performed by use of a master carrier including a signal pattern in which a length L of a sequence of a direct-current signal is supposed to be equal to or longer than about 10 times of a half-width W of a isolated waveform in a readout waveform as shown in FIG. 4C, there is a possibility that a slave medium after the magnetic transfer causes the above-described subpulse in a direct-current signal area in a position immediately before transition from the direct-current signal to the solitary waveform.